In general, with tightening of emission control, an aftertreatment apparatus for purifying an exhaust gas takes a growing interest. In particular, the emission control is being more tightened on particulate matter (PM) from a diesel car.
Specifically, the emission control on exhaust pollutant included in the exhaust gas is increasingly tightened due to a demand on a healthy environment and an environmental regulation of each country against air pollutant, and as a countermeasure for this situation, various exhaust gas purification methods are being studied.
To this end, an aftertreatment technology for treating the exhaust gas has been proposed, which includes exhaust gas reduction apparatuses employing oxidation catalyst, nitrogen oxide catalyst, and diesel particulate filter.
Among the above-mentioned exhaust gas reduction apparatuses employing the oxidation catalyst, the nitrogen oxide catalyst, and the diesel particulate filter, the most efficient and commercially-available technology is the exhaust gas reduction apparatus employing the diesel particulate filter.
In order to diagnose malfunctioning of the exhaust gas reduction apparatus, a resistor-type particulate matter sensor (PM sensor) is installed at a post-stage of the DPF filter. That is, the particulate matter (PM) is deposited between electrodes on a surface of the sensor, due to which a current is generated between the electrodes and electrical conductivity of the sensor is changed.
However, such a resistor-type particulate matter sensor has a very slow response speed at the initial stage until the current is generated, and when a particulate matter having the electrical conductivity, such as a metal, is deposited on the surface, generates a distortion of a signal regardless of the amount of the particulate matter, which causes malfunctioning of the sensor.
Patent Document 1: Japanese Patent Application Laid-Open No. 2009-85959 (Publication Date: Apr. 23, 2009)